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Page:Popular Science Monthly Volume 44.djvu/352

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340
THE POPULAR SCIENCE MONTHLY.

the brake, and a third on the grating outside to handle the sinker and instruments and to guide the wire as it passes overboard; a machinist is at the hoisting engine, and the recorder takes a position for reading the register. When the sinker is let go, the vessel is manœuvred so as to keep the wire vertical, and the friction line is adjusted so as to allow it to descend from seventy to one hundred fathoms per minute. The instant the sinker strikes bottom,

PSM V44 D352 The sinker is lowered for sounding.jpg
Fig. 6.—Sounding: The Sinker going down.

which is unmistakably indicated by the sudden release of the wire from strain, the reel is stopped by the friction line and brake; the recorder notes the number of turns of the reel indicated by the register and determines the depth; the cranks are shipped and sufficient wire is hove in by hand to allow the end of the sounding rod to clear the bottom. Steam is then admitted to the cylinder of the hoisting engine, and the wire is reeled in slowly at first but finally at the rate of one hundred to one hundred and fifty fathoms per minute. The last ten fathoms are reeled in by hand, then the thermometer is read and the specimen of the bottom soil brought up in the sounding cylinder is examined.